Structure for electrostatic discharge in embedded wafer level packages

ABSTRACT

A workpiece has at least two semiconductor chips, each semiconductor chip having a first main surface, which is at least partially exposed, and a second main surface. The workpiece also comprises an electrically conducting layer, arranged on the at least two semiconductor chips, the electrically conducting layer being arranged at least on regions of the second main surface, and a molding compound, arranged on the electrically conducting layer.

BACKGROUND OF THE INVENTION

The invention relates to a workpiece with semiconductor chips, such as for example a panel with semiconductor chips arranged in semiconductor device positions. It also relates to a semiconductor device and to a method for producing the workpiece.

In the production of semiconductor devices, successful results have been obtained with methods in which a composite panel or so-called “reconfigured wafer” is first produced by the “wafer molding” process from semiconductor chips that are embedded with a main surface and side faces in a plastic molding compound. First main surfaces of the semiconductor chips thereby form a coplanar surface with the upper side of the plastic compound or the first main surface of the composite panel or of the “reconfigured wafer”. A wiring structure is then applied to this coplanar surface, it being possible for the plastic surface around the front side of each semiconductor chip to be used for accommodating additional terminals or for arranging contact terminal areas of any desired sizes and spacings.

In the case of such a method, electrostatic discharges (ESD) may occur, and may cause damage to the semiconductor chips or even their destruction. Furthermore, the semiconductor chips of semiconductor devices should be protected from disturbing influences of electromagnetic radiation.

SUMMARY OF THE INVENTION

According to an embodiment of the invention, a workpiece which comprises at least two semiconductor chips is provided, each semiconductor chip having a first main surface, which is at least partially exposed, and a second main surface. The workpiece also comprises an electrically conducting layer arranged on the at least two semiconductor chips, the electrically conducting layer being arranged at least on regions of the second main surface, and a molding compound being arranged on the electrically conducting layer.

Embodiments of the invention are now described with reference to the accompanying figures.

FIG. 1 schematically shows a step of a method for producing a workpiece according to one aspect of the invention;

FIG. 2 schematically shows a further step of the method for producing a workpiece;

FIG. 3 schematically shows a further step of the method for producing a workpiece;

FIG. 4 schematically shows a section through the workpiece;

FIG. 5 schematically shows a plan view of the workpiece;

FIG. 6 schematically shows a cross section through a semiconductor device according to one aspect of the invention;

FIG. 7 shows a cutout from the semiconductor device according to FIG. 6;

FIG. 8 schematically shows a step of a method for producing a workpiece according to a second embodiment of the invention;

FIG. 9 schematically shows a further step of the method for producing a workpiece according to the second embodiment;

FIG. 10 schematically shows a further step of the method for producing a workpiece according to the second embodiment;

FIG. 11 schematically shows a section through the workpiece according to the second embodiment;

FIG. 12 schematically shows a further step of the method for producing a workpiece according to the second embodiment;

FIG. 13 schematically shows a further step of the method for producing a workpiece according to the second embodiment;

FIG. 14 schematically shows a further step of the method for producing a workpiece according to the second embodiment and

FIG. 15 schematically shows a cross section through a finished semiconductor device according to the second embodiment of the invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The same parts are provided with the same designations in all the figures.

FIG. 1 shows a carrier sheet 3, on the upper side 4 of which semiconductor chips 1 have been applied in semiconductor device positions 2 that are arranged in rows and columns to produce a workpiece, which in this embodiment is a panel. In this context, “workpiece” is understood as meaning an article that is still intended for further processing, for example an intermediate product in the production of semiconductor devices, such as a panel. The semiconductor chips 1 have previously been singulated from a semiconductor wafer. Interspaces 16 are formed between the semiconductor chips 1.

In this exemplary embodiment, the semiconductor chips 1 have first main surfaces 5 with active semiconductor chip structures such as integrated circuits and contact areas 6. The side faces 7 and the second main surfaces 8 of the semiconductor chips 1 are passive. Alternatively, active regions may also be arranged on the second main surface of the semiconductor chips or on the first and second main surfaces.

A further method step is represented in FIG. 2. An electrically conducting layer 9 is applied to regions of the second main surfaces 8 and the side faces 7 of the semiconductor chips 1. In the exemplary embodiment represented, the electrically conducting layer 9 thereby also covers regions of the upper side 4 of the carrier 3 in the interspaces 16 between the semiconductor chips and in this way connects the semiconductor chips 11 to one another in an electrically conducting manner. In an exemplary embodiment that is not shown, the electrically conducting layer 9 is not applied directly to the side faces 7, but instead an intermediate layer is arranged between the side faces 7 and the electrically conducting layer 9 and may be formed for example like a ramp. Such a ramp can facilitate uniform application of the electrically conducting layer 9.

The electrically conducting layer 9 typically has a thickness d of less than 100 μm, if it is produced from a filled or electrically conducting polymer. Layer thicknesses of 20 μm≦d≦50 μm are advantageous for example. If the electrically conducting layer 9 is produced from a metal, it typically has a layer thickness d of a few micrometers or tenths of a micrometer, for example 0.1 μm≦d≦2 μm.

At least in regions in the interspaces 16, the electrically conducting layer 9 has interfaces with the carrier 3. In a later stage of the method, when the carrier 3 is removed, these interfaces become exposed contact regions 15, by means of which the electrically conducting layer 9 is accessible for electrical contacting.

In a further method step, as represented in FIG. 3, the semiconductor chips 1 are embedded with their side faces 7 and their second main surfaces 8 in a molding compound 10. In this way, the workpiece 12 is obtained as a composite sheet comprising semiconductor chips 1, molding compound 10 and electrically conducting layer 9.

In the case where the electrically conducting layer 9 is applied as a closed layer, the carrier sheet 3 is covered by the electrically conducting layer 9 in the entire region of the interspaces 16. A closed layer is understood here as meaning a layer that is applied over a large surface area and covers the main part of the first main surface 11 of the workpiece 12 outside chip regions that are defined by the first main surfaces of the semiconductor chips. In this case, after removal of the carrier sheet 3, the first main surfaces 5 of the semiconductor chips 1 and regions of the electrically conducting layer 9 on the first main surface 11 of the workpiece 12 are exposed, but no molding compound 10 is exposed.

In an alternative embodiment, however, the electrically conducting layer 9 is formed as a grid structure and only covers regions of the second main surfaces 8 and possibly of the side faces 7 and the interspaces 16. The grid structure in this case comprises for example rows and columns of the electrically conducting layer 9, the grid being so closely meshed that there is at least one column respectively crossing a row on the second main surface 8 of a semiconductor chip 1. In this case, the molding compound 10 penetrates inbetween, to the upper side 4 of the carrier sheet 3, and after removal of the carrier sheet 3 is exposed on the front side 11 of the workpiece 12.

The front side 11 of the workpiece 12 is consequently a coplanar surface comprising the first main surfaces 5 of the semiconductor chips 1 in the semiconductor device positions 2, contact regions 15 of the electrically conducting layer 9 and possibly molding compound 10.

The electrically conducting layer 9 is formed for example from a conductive polymer, a metal or a plastic with electrically conducting particles. Application is performed, for example, by printing on a conductive polymer or a conductive ink, by vapor deposition, by sputtering or by placing on a metal mesh or a netting or a gauze-like fabric of a conductive polymer.

A thermoplastic or thermosetting material is provided as the molding compound 10, and is applied for example by injection-molding onto the electrically conducting layer 9.

FIG. 4 schematically shows a cross section through the workpiece 12 produced, after removal of the carrier sheet 3. The first main surfaces 5 of the semiconductor chips 1, which in this embodiment have active structures, are exposed on the first main surface 11 of the workpiece 12. The first main surface 11 of the workpiece 12 is a coplanar surface comprising the first main surfaces 5 of the semiconductor chips 1, contact regions 15 of the electrically conducting layer 9 and possibly molding compound 10. In the contact regions 15, the electrically conducting layer 9 is exposed on the first main surface 11 of the workpiece 12 and can be contacted for discharging the workpiece 12 or for preventing electrostatic charging. The second main surface 34 of the workpiece 12 is formed by the molding compound 10.

FIG. 5 shows a plan view of the first main surface 11 of the workpiece 12 after removal of the carrier sheet 3. In this exemplary embodiment, the workpiece is formed as a panel with semiconductor chips 1 arranged in rows and columns, which has the form and the dimensions of a semiconductor wafer. In this embodiment, the electrically conducting layer 9 has been applied in continuous strips 25, which follow in their direction the rows 14 and columns 13 in which the semiconductor chips 1 are arranged in the semiconductor device positions 2. In this case, two strips 25 from directions perpendicular to each other respectively cross on the second main surface 8 of a semiconductor chip 1, with the result that the electrically conducting layer 9 forms a grid, semiconductor chips 1 respectively being arranged on the grid points. In this way, all the semiconductor chips 1 of a panel can be conductively connected to one another in a simple way.

The conductive strips 25, which respectively form the rows 14 and columns 13, are exposed in the interspaces 16 between the semiconductor chips 1 on the first main surface 11 of the workpiece 12, where they form contact regions 15. Since, however, only these conductive strips 25 are exposed, and the remaining surface area of the first main surface 11 of the workpiece 12 that is not taken up by the first main surfaces 5 of the semiconductor chips 1 is formed by molding compound 10, adequate electrically insulating surface area is available for the arrangement of other elements, for example external contact areas for semiconductor devices.

The first main surface 11 of the workpiece 12 is a coplanar surface comprising the first main surfaces 5 of the semiconductor chips 1, regions of the molding compound 10 and contact regions 15 of the electrically conducting layer 9, it being possible for all the semiconductor chips 1 to be electrically contacted by means of the contact regions 15. After the removal of the carrier sheet 3, a wiring structure with interconnects and external contacts can be applied to the then exposed first main surface 11 of the workpiece 12.

In the embodiment shown, the electrically conducting layer 9 is formed as a grid structure. In an exemplary embodiment that is not shown, the grid is more closely meshed, with the result that a number of rows 14 and columns 13 respectively cross on the second main surface 8 of a semiconductor chip 1.

However, the electrically conducting layer 9 may also be differently formed, for example as a substantially closed layer. A closed layer has the advantage that it can be applied particularly simply. However, in this case the entire, or virtually entire, region of the first main surface 11 of the workpiece 12 that is not taken up by the first main surfaces 5 of the semiconductor chips 1 is covered by the conductive layer 9. In order to form wiring structures and/or external contacts on it, an insulating layer must first be applied again, it being possible for contact regions 15 to be left exposed.

The contact regions 15 permit the electrical contacting of all, or at least many, of the semiconductor chips 1, which are connected to one another in an electrically conducting manner to form a contact group. This allows electrostatic charges of the workpiece 12, for example a panel, to be prevented or dissipated as quickly as possible during processing. As a result, it is not necessary to handle and process devices that are susceptible to ESD only in a specially protected environment, for which relatively complex devices are required, such as ionizers for generating ionized ambient air and electrically conductive work surfaces that prevent electrostatic charging of the devices as completely as possible.

Instead, low charges of the workpiece 12 during processing are specifically dissipated before they reach a critical value, by contacting of the electrically conducting layer 9 in the contact regions 15. For this purpose, the semiconductor chips 1 in the workpiece 12 are conductively connected to one another by a discharge structure in the form of the electrically conducting layer 9, and contact regions 15 on the first main surface 11 of the workpiece 12 are created to allow easy access to the entire discharge structure, with the result that a potential equalization can take place at any time during processing to dissipate possible charges.

If the electrically conducting layer 9 is contiguous, single contacting is sufficient to discharge the entire workpiece 12. If, on the other hand, the workpiece 12 is to be discharged region by region, for example row by row or column by column, the electrically conducting layer may also be made up of a number of partial regions that are insulated from one another.

With the method described, the application of a possibly structured discharge structure, and in particular contacting of the second main surface 8 of the semiconductor chips 1 by the electrically conducting layer 9 is possible in a single step on the entire workpiece 12. This is accompanied by an enormous saving in terms of time and cost and in this way makes laborious precautions for a specially protected environment unnecessary.

Since, with potential equalization, only relatively small currents are expected, the resistance of the electrically conducting layer 9 may also be greater than that of a metallic layer. Therefore, not only metals are conceivable as materials for the layer 9, but also for example electrically conducting polymers or plastics with electrically conducting particles. This has the advantage that the material for the layer 9 can be selected on the basis of other criteria, for example on the basis of easy applicability and processability.

FIG. 6 schematically shows a cross section through a semiconductor device 17, which has been singulated from the workpiece 12 according to FIGS. 4 and 5, for example by sawing along dicing tracks that are not shown.

The semiconductor device 17 has a semiconductor chip 1, which is embedded with its side faces 7 and its second main surface 8 in a molding compound 10. An electrically conducting layer 9 is arranged along the semiconductor chip contour on the side faces 7 and the first main surface 8. In the case of this exemplary embodiment, only regions of the first main surface 26 of the semiconductor device 17 are formed by contact regions of the electrically conducting layer 9, these contact regions not being visible in the sectional view that is shown. The second main surface 37 of the semiconductor device 17 is formed by the molding compound 10.

The semiconductor device has on its first main surface 26 a wiring layer 18, which is typically multilayered, and external contacts 19. The cutout 20 is represented in detail in FIG. 7.

FIG. 7 shows the cutout 20 from FIG. 6. It can be seen from this that the wiring layer 18 in this case comprises three layers, to be specific one layer of a dielectric 22 directly on the first main surface 5 of the semiconductor chip 1 or on the first main surface 26 of the semiconductor device 17, an electrically conductive layer on that, which forms interconnects 23, and a further insulating layer of a dielectric 24.

In the contact region 15, the electrically conducting layer 9 butts against the first main surface 26 of the semiconductor device 17. At this point, the interconnect 23 is in electrical contact with the electrically conducting layer 9. In this way, the electrically conducting layer can be contacted by means of the external contacts of the semiconductor device 17 also in the case of the finished semiconductor device 17, in which the contact regions 15 themselves are no longer exposed. The molding compound 10 covering the electrically conducting layer 9 forms a plastic package for the semiconductor device 17.

FIG. 8 schematically shows a step of a method for producing a workpiece according to a second embodiment of the invention. It is also the case with this embodiment that, in a first method step, a number of semiconductor chips 1 are applied with their first main surfaces 5 onto the upper side 4 of a carrier sheet 3, interspaces 16 being arranged between the semiconductor chips 1.

FIG. 9 shows a further step of the method according to the second embodiment. An insulating layer 27 of an electrically insulating material is first arranged on the second main surfaces 8 of the semiconductor chips 1, and possibly also on the side faces 7. Parylene or polyimide is used for example as the insulating material. The insulating layer 27 may, for example, be vapor-deposited or applied by placing on an electrically insulating film.

The depositing of a parylene layer as an insulating layer 27 is performed for example by gas-phase polymerization: firstly, the dimer of the compound is vaporized. The dimer is prepared for example by dehydrating pyrolitic dimerization of p-xylene and subsequent quenching in liquid p-xylene. In this way, [2,2]-p-cyclophane is obtained. In the subsequent pyrolysis of the dimer, the dimer splits into two bivalent radical monomers such as p-xylene. During the deposition of the monomers, which are in the gas phase, on the surfaces to be coated, the polymerization takes place on cooling. By this process, a very pure parylene coating can be deposited. The vaporization is carried out for example at a temperature of 160° C. to 180° C. and a pressure of 1-2 mbar and the pyrolysis is carried out at a temperature of 660° C. to 690° C. and a pressure of 0.5-1 mbar. The polymerization takes place for example at a temperature of less than 35° C. and a pressure of 0.1-0.2 mbar. This process permits very uniform deposition of the insulating layer 27, which as a result has virtually the same thickness in all regions.

Subsequently, the electrically conducting layer 9 is applied to the insulating layer 27, with the result that the insulating layer 27 is arranged between the semiconductor chips 1 and the electrically conducting layer 9. It is also the case with this embodiment that the electrically conducting layer 9 may be formed from a conductive polymer, a metal or a plastic with electrically conducting particles. Application is likewise performed, for example, by printing on a conductive polymer or a conductive ink, by vapor deposition, by sputtering or by placing on a metal mesh or a netting or a gauze-like fabric of a conductive polymer.

In the case of this embodiment, the electrically conducting layer 9 forms an electromagnetic shielding of the semiconductor chips 1. Such a shielding protects the semiconductor chips 1 from disturbing influences of electromagnetic radiation, which is necessary in particular in the case of applications such as baseband processors, power management units or radio-frequency circuits.

In a further method step, the result of which is shown in FIG. 10, a molding compound 10 is arranged on the electrically conducting layer 9, with the result that the second main surface 34 of the workpiece 12 is formed by the molding compound 10. A thermoplastic or thermosetting material, which is applied to the electrically conducting layer 9 by injection molding, for example, is provided as the molding compound 10. In the embodiment shown, the side faces 7 and the second main surfaces 8 of the semiconductor chips 1 are embedded in the molding compound 10.

In the embodiment represented, the workpiece 12 is formed as a panel with semiconductor chips 1 arranged in rows and columns at semiconductor device positions 2. The method described according to the second embodiment makes it possible to apply the electromagnetic shielding to all the semiconductor chips 1 of a panel already at the wafer level. The shielding is accordingly firmly integrated in the package of the semiconductor devices, with the result that a particularly compact semiconductor device and at the same time a particularly simple production method can be provided.

In a further method step, the result of which is shown in FIG. 11, the carrier sheet 3 is removed, with the result that the first main surfaces 5 of the semiconductor chips 1 and regions 28 of the insulating layer 27, which together form a coplanar surface and the first main surface 11 of the workpiece 12, are exposed. Then, as described above, a wiring layer is applied to the exposed first main surface 11.

FIG. 12 schematically shows a further method step according to the second embodiment. The carrier sheet has already been removed from the first main surface 11 of the workpiece 12 and a dielectric layer 31 has been applied as part of a wiring layer to the first main surface 11. In the dielectric layer 31, vias 29 or through-holes for shielding and vias 30 to contact areas 6 of the semiconductor chips 1 are opened, for example by a (dry or wet) etching process or by laser ablation.

FIG. 13 shows a further method step, in which a metallization 32 is applied as part of a wiring layer. With the metallization 32, the electrically conducting layer 9 is contacted through the vias 29 and the contact areas 6 of the semiconductor chips 11 are contacted through the vias 30. Furthermore, external contact areas 35 for applying external contacts are formed.

FIG. 14 shows a subsequent method step, in which a solder resist layer 33 has been applied to the dielectric layer 31 and structured, in order to leave the external contact areas 35 exposed for applying external contacts. External contacts 19 are applied to the external contact areas 35, for example in the form of solder balls. The workpiece 12 can subsequently be divided up along dicing tracks, which are indicated by the dashed lines 36, into individual semiconductor devices, for example by sawing.

A completed semiconductor device 17 according to the second embodiment of the invention is shown in FIG. 15. In this embodiment, the semiconductor device 17 has a semiconductor chip 1 with the first main surface 5, the second main surface 8 and the side faces 7. The electrically conducting layer 9 arranged on the semiconductor chip 1, which layer is arranged at least on regions of the second main surface 8, forms an electromagnetic shielding of the semiconductor chips 1. The insulating layer 27 is arranged between the semiconductor chip 1 and the electrically conducting layer 9. Arranged on the electrically conducting layer 9 is the molding compound 19, which forms the plastic package of the semiconductor device 17.

In the case of the semiconductor device 17, regions 28 of the insulating layer 27 form a coplanar surface with the first main surface 5 of the semiconductor chip 1 on a first main surface 26 of the semiconductor device 17.

The first main surface 26 of the semiconductor device 17 has a wiring structure or wiring layer 18, which comprises at least the dielectric layer 31, the metallization 32 with the external contact areas 35 and the solder resist layer 33. The wiring layer 18 may, however, also be of a multilayered form and have a number of metallization layers and further contact vias. By means of the external contacts 19, the electrically conducting layer 9 can also be electrically contacted and connected to a predetermined potential. It is also the case in this embodiment that the second main surface 37 of the semiconductor device 17 is formed by the molding compound 10. 

1. A method for producing a workpiece, comprising: providing at least two semiconductor chips each having a first main surface and a second main surface; placing the semiconductor chips with their first main surfaces on the upper side of a carrier sheet; applying an electrically conducting layer to regions of the second main surfaces, the electrically conducting layer being in the form of a grid structure comprising rows and columns of electrically conducting material, with the semiconductor chips being respectively arranged at intersecting points of the rows and columns; applying a molding compound to the electrically conducting layer; and removing the carrier sheet, thereby exposing the first main surface of the semiconductor chips and molding compound that is co-planar with the first main surface of the semiconductor chips.
 2. The method of claim 1, further comprising applying the electrically conducting layer to regions of an upper side of the carrier sheet in interspaces between the semiconductor chips.
 3. The method of claim 1, further comprising applying the electrically conducting layer to side faces of the semiconductor chips.
 4. The method of claim 1, further comprising applying the electrically conducting layer by printing on a conductive polymer or a conductive ink.
 5. The method of claim 1, further comprising applying the electrically conducting layer by vapor-depositing.
 6. The method of claim 1, further comprising applying the electrically conducting layer by sputtering.
 7. The method of claim 1, further comprising arranging the electrically conducting layer such that the semiconductor chips are connected to one another in an electrically conducting manner.
 8. The method of claim 1, further comprising applying an insulating layer of an electrically insulating material to regions of the semiconductor chips before applying the electrically conducting layer.
 9. The method of claim 8, further comprising vapor-depositing the insulating layer.
 10. The method of claim 8, further comprising placing the insulating layer on an electrically insulating film.
 11. The method of claim 1, further comprising dividing up the panel into semiconductor devices along dicing tracks.
 12. The method of claim 1, further comprising applying the electrically conducting layer such that the grid structure is made up a number of partial regions that are insulated from one another.
 13. The method of claim 12, wherein one partial region comprises a predetermined row or a plurality of predetermined rows of the grid structure.
 14. The method of claim 12, wherein one partial region comprises a predetermined column or a plurality of predetermined columns of the grid structure. 